Method of manufacturing semiconductor device

ABSTRACT

A method of manufacturing a semiconductor device by performing a process on a substrate includes: forming a protective layer made of a polymer having a urea bond by supplying a raw material for polymerization to a surface of a substrate on which a protected film to be protected is formed; forming a sealing film at a first temperature lower than a second temperature at which the polymer is depolymerized so cover a portion where the protective layer is exposed; subsequently, subjecting the substrate to a treatment at a third temperature equal to or higher than the second temperature at which the polymer as the protective layer is depolymerized; subsequently, performing a treatment which causes damage to the protected film when the protective layer is not present; and after the performing a treatment which causes damage to the protected film, depolymerizing the polymer by heating the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2017-068759, filed on Mar. 30, 2017, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a technique of suppressing damage byforming a protective layer on a film formed on a substrate formanufacturing a semiconductor device.

BACKGROUND

In a process of manufacturing a semiconductor device, if the processingof a substrate is not carefully performed, the film previously formed onthe substrate may be damaged. For example, when a plasma treatment suchas etching or ashing is performed on a porous low dielectric constantfilm used as an interlayer insulating film in order to embed a wiring,the low dielectric constant film is damaged. Specifically, the porouslow dielectric constant film is, for example, a SiOC film containingsilicon, carbon, oxygen and hydrogen and having Si—C bonds. On anexposed surface of the SiOC film exposed to plasma, namely on a sidewall and a bottom surface of a recess, for example, the Si—C bonds arebroken by plasma and C is desorbed from the film. Si having unsaturatedbonds generated due to desorption of C is unstable in that state. Thus,Si is bonded to, for example, moisture in the atmosphere, to becomeSi—OH constituting a damaged layer.

For example, a technique has been used in which a PMMA (acrylic resin)is embedded in advance in pores of a porous low dielectric constant filmformed on a substrate, a process such as etching or the like isperformed on the low dielectric constant film, the substrate is heated,a solvent is supplied, and a microwave is supplied to remove the PMMA.However, in order to remove the PMMA, it is necessary to spend a longperiod of time of about 20 minutes in a plasma treatment and to heat thesubstrate to a temperature of 400 degrees C. or higher. Therefore, thereis a great concern that element portions already formed in the substratemay be adversely affected.

As another example, there is an example in which, in a process ofmanufacturing a memory element, a surface (interface) of an electrodefilm is oxidized to form a damaged layer as an oxide layer when acontact hole is formed by a plasma treatment. In this process, first, anelectrode film and a mask (etching mask) film are laminated on a memoryelement film, for example, a metal oxide film, to form a laminate. Then,the laminate is etched. Subsequently, an insulating film is formed onthe substrate. The laminate left by etching is buried in the insulatingfilm. Then, the insulating film on the laminate is etched by the plasmatreatment to form the contact hole.

In the plasma treatment, the mask film is over-etched, and a damagedlayer (oxide layer) is formed at the interface of the electrode film.Thus, for example, a reduction treatment is performed by hydrogenannealing or the like. However, there is a possibility that the removalof the damaged layer becomes insufficient even if the reductiontreatment is performed.

Furthermore, in the concept of thermal decomposition of a resin, it isknown that as the resin removal temperature decreases, a heat resistanttemperature of the resin also decreases. It is also known that only aPMMA can be thermally unstuffed at 400 degrees C., which is an allowabletemperature in a wiring process. However, the thermal stability of thePMMA drops to 250 degrees C. This means that if a temperature of 250degrees C. or higher is applied to the PMMA during a protection processusing the PMMA, a PMMA film deteriorates so that it cannot be used as aprotective film.

Therefore, the technique described above is not a technique in which aprotective film functions as a protective film even when a thermalprocess is performed at a temperature exceeding a protective filmremoval temperature as in the present disclosure.

SUMMARY

Some embodiments of the present disclosure provide a technique capableof suppressing damage on a film which is formed on a substrate in orderto manufacture a semiconductor device.

According to one embodiment of the present disclosure, there is provideda method of manufacturing a semiconductor device by performing a processon a substrate, including: forming a protective layer made of a polymerhaving a urea bond by supplying a raw material for polymerization to asurface of a substrate on which a protected film to be protected isformed; forming a sealing film at a first temperature lower than asecond temperature at which the polymer is depolymerized, so as to covera portion where the protective layer is exposed; after the forming asealing film, subjecting the substrate to a treatment at a thirdtemperature equal to or higher than the second temperature at which thepolymer as the protective layer is depolymerized; after the subjectingthe substrate to a treatment at a third temperature, performing atreatment which causes damage to the protected film when the protectivelayer is not present; and after the performing a treatment which causesdamage to the protected film, depolymerizing the polymer by heating thesubstrate.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the presentdisclosure, and together with the general description given above andthe detailed description of the embodiments given below, serve toexplain the principles of the present disclosure.

FIGS. 1A to 1D are explanatory views showing some steps of asemiconductor device manufacturing method according to a firstembodiment of the present disclosure.

FIGS. 2E to 2H are explanatory views showing some steps of thesemiconductor device manufacturing method according to the firstembodiment of the present disclosure.

FIGS. 3I to 3L are explanatory views showing some steps of thesemiconductor device manufacturing method according to the firstembodiment of the present disclosure.

FIGS. 4M to 4P are explanatory views showing some steps of thesemiconductor device manufacturing method according to the firstembodiment of the present disclosure.

FIGS. 5Q to 5S are explanatory views showing some steps of thesemiconductor device manufacturing method according to the firstembodiment of the present disclosure.

FIG. 6 is an explanatory view showing how a polymer having a urea bondis produced by self-polymerization using isocyanate and water.

FIGS. 7A to 7D are explanatory views showing stepwise a process ofproducing a polymer having a urea bond by self-polymerization usingisocyanate and water.

FIG. 8 is a molecular structure diagram showing a molecular structure ofan example of isocyanate.

FIG. 9 is a sectional view showing an apparatus for supplying isocyanateliquid to a substrate.

FIG. 10 is a sectional view showing an apparatus for supplying watervapor to a substrate to which isocyanate liquid has been supplied.

FIG. 11 is a sectional view showing a heating apparatus for heating asubstrate to which isocyanate and water vapor have been supplied.

FIG. 12 is an explanatory view showing how a polymer having a urea bondis produced by a copolymerization reaction.

FIGS. 13A to 13D are explanatory views showing a reaction in which apolymer having a urea bond becomes an oligomer.

FIGS. 14A and 14B are explanatory views showing how a polymer having aurea bond is produced using a secondary amine.

FIG. 15 is an explanatory view showing how a polymer having a urea bondis produced by cross-linking monomers having a urea bond.

FIG. 16 is a sectional view showing an apparatus for producing a polymerhaving a urea bond by reacting isocyanate and amine with water vapor

FIGS. 17A to 17D are explanatory views showing some steps of asemiconductor device manufacturing method according to a secondembodiment of the present disclosure.

FIGS. 18E to 18H are explanatory views showing some steps of thesemiconductor device manufacturing method according to the secondembodiment of the present disclosure.

FIGS. 19I to 19K are explanatory views showing some steps of thesemiconductor device manufacturing method according to the secondembodiment of the present disclosure.

FIG. 20 is a sectional view showing an apparatus for supplyingisocyanate liquid and amine liquid to a substrate.

FIG. 21 is a characteristic diagram showing absorption spectra beforeand after embedment of polyurea in a low dielectric constant film.

FIG. 22 is a characteristic diagram showing absorption spectra afteroverlapping and heating two substrates on which a polyurea film isformed.

FIG. 23 is a characteristic diagram showing the relationship between afilm thickness of a polyurea film and a heating temperature.

FIG. 24 is a characteristic diagram showing the measurement results ofabsorption spectra of a polyurea film after heating for each filmthickness of a polyimide film formed on the polyurea film.

FIG. 25 is a characteristic diagram showing the relationship between aresidual ratio of CH bonds of a polyurea film after heating and aheating temperature for each film thickness of a polyimide film formedon the polyurea film.

FIG. 26 is a characteristic diagram showing the relationship between afilm thickness of a polyimide film formed on a polyurea film and aresidual ratio of CH bonds and NH bonds of the polyurea film afterheating.

FIG. 27 is a characteristic diagram showing the relationship between afilm thickness after heating and a residual ratio of CH bonds for asingle polyurea film.

FIG. 28 is a characteristic diagram showing the relationship between afilm thickness and a residual ratio of CH bonds and NH bonds of apolyurea film after heating for the single polyurea film.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments, examples ofwhich are illustrated in the accompanying drawings. In the followingdetailed description, numerous specific details are set forth in orderto provide a thorough understanding of the present disclosure. However,it will be apparent to one of ordinary skill in the art that the presentdisclosure may be practiced without these specific details. In otherinstances, well-known methods, procedures, systems, and components havenot been described in detail so as not to unnecessarily obscure aspectsof the various embodiments.

An embodiment in which a semiconductor device manufacturing methodaccording to the present disclosure is applied to a process of forming awiring of a semiconductor device by dual damascene will be described.FIGS. 1A to 3L are explanatory views showing stepwise how to form anupper-layer-side circuit portion on a lower-layer-side circuit portion.Reference numeral 11 denotes, for example, an interlayer insulating filmformed at the lower layer side, reference numeral 12 denotes a copperwiring which is a wiring material embedded in the interlayer insulatingfilm 11, and reference numeral 13 denotes an etching stopper film havinga function of a stopper at the time of etching. The etching stopper film13 is formed of, for example, SiC (silicon carbide), SiCN (siliconcarbide nitride), or the like.

A low dielectric constant film 20 as an interlayer insulating film isformed on the etching stopper film 13. In this example, a SiOC film isused for the low dielectric constant film 20. The SiOC film is formed bya CVD method, for example, by converting DEMS (diethoxymethylsilane)into plasma. The low dielectric constant film 20 is porous. In FIGS. 1Ato 3L, pores 21 in the low dielectric constant film 20 are shownschematically with emphasis. A SiOC film is also used for the interlayerinsulating film 11 formed at the lower layer side.

In the method of the present embodiment, as shown in FIG. 1A, thelower-layer-side circuit portion is formed on the surface of asemiconductor wafer (hereinafter referred to as wafer), which is asubstrate. The porous low dielectric constant film 20 is formed on thelower-layer-side circuit portion. Processing is started in this state.In this example, the low dielectric constant film 20 corresponds to aprotected film.

In the present embodiment, the pores 21 in the low dielectric constantfilm 20 are filled with a polymer (polyurea) having urea bonds, which isa filling material, as described below. The polyurea embedded in thepores 21 in the low dielectric constant film 20 corresponds to aprotective layer for protecting the low dielectric constant film 20 as aprotected film from the plasma in a plasma treatment described later. Asa method for producing the polyurea, there is available a technique suchas copolymerization or the like as described later. In this example, atechnique of producing the polymer by self-polymerization will bedescribed.

First, isocyanate (liquid), which is a raw material ofself-polymerization, is impregnated into the low dielectric constantfilm 20 (FIG. 1B), and then the low dielectric constant film 20 isimpregnated with moisture, for example, water vapor (FIG. 1C). Whenisocyanate is reacted with moisture, the isocyanate is hydrolyzed toimmediately produce polyurea, and the pores 21 of the low dielectricconstant film 20 are filled with the polyurea. FIG. 6 shows such areaction. A portion of the isocyanate becomes amine which is an unstableintermediate product. The intermediate product and the non-hydrolyzedisocyanate are reacted with each other to produce polyurea. In FIG. 6, Ris, for example, an alkyl group (linear alkyl group or cyclic alkylgroup) or an aryl group, and n is an integer of two or more.

As the isocyanate, for example, an alicyclic compound, an aliphaticcompound, an aromatic compound or the like may be used. As the alicycliccompound, for example, 1,3-bis (isocyanatomethyl) cyclohexane (H6XDI)may be used as shown in FIG. 7A described later. As the aliphaticcompound, for example, hexamethylene diisocyanate may be used as shownin FIG. 8. The isocyanate may have a melting point of 100 degrees C. orless and may be liquid at room temperature.

FIGS. 7A to 7D are explanatory views schematically showing the state ofa process using H6XDI as a raw material monomer, in which treatmentsperformed on a wafer W and chemical formulae are associated with oneanother. FIG. 7A corresponds to a process of supplying isocyanate to thewafer W, which is shown in FIG. 1B. First, by spin-coating the liquid ofH6XDI on the wafer W, the liquid is impregnated into the low dielectricconstant film 20.

As a spin coating apparatus for performing the spin coating, forexample, an apparatus shown in FIG. 9 may be used. In FIG. 9, referencenumeral 31 denotes a vacuum chuck which is rotated by a rotationmechanism 30 while adsorptively holding the wafer W, reference numeral32 denotes a cup module, and reference numeral 33 denotes a guide memberhaving a cylindrical outer peripheral wall and a cylindrical innerperipheral wall which extend downward. Reference numeral 34 denotes adischarge space formed between an outer cup 35 and the outer peripheralwall so that exhaust and drainage can be performed over the entirecircumference. The lower side of the discharge space 33 has a structurecapable of gas-liquid separation. The liquid is supplied from a liquidsupply source 37 to the central portion of the wafer W via a nozzle 36.The wafer W is rotated at a rotation speed of, for example, 1,500 rpm,to spread the liquid on the surface of the wafer W, thereby forming acoating film.

Subsequently, placing the wafer W in a heated atmosphere of 80 degreesC. and in a water vapor atmosphere (relative humidity 100%), water vaporpermeates into the low dielectric constant film 20. FIG. 7B correspondsto a process of supplying water vapor as moisture to the wafer W, asshown in FIG. 1C.

For example, the apparatus shown in FIG. 10 may be used as an apparatusfor performing the water vapor treatment. In FIG. 10, reference numeral41 denotes a processing container in which a water vapor atmosphere isestablished, reference numeral 42 denotes a water vapor generation part,reference numeral 43 denotes a water vapor discharging part having alarge number of holes formed in the lower surface thereof, referencenumeral 44 denotes a conduit for guiding water vapor to a diffusionspace defined inside the water vapor discharge part 43, referencenumeral 45 denotes a mounting table incorporating a heater 46, andreference numeral 47 denotes an exhaust pipe from which a gas isexhausted by a suction mechanism. An inner wall of the processingcontainer 41 is heated to, for example, 80 degrees C. by a heatingmechanism (not shown). The wafer W is mounted on the mounting table 45and is exposed to an atmosphere of the water vapor discharged from thewater vapor discharge part 43.

As the apparatus for performing the water vapor treatment, it may bepossible to adopt a configuration in which, instead of providing thewater vapor generation part 42 and the water vapor discharge part 43, aflat container with a lid is provided above the mounting table 45, andthe flat container is heated with water accommodated therein so that theinterior of the processing container is kept in the water vaporatmosphere. In this case, when loading and unloading the wafer W, theflat container is opened and closed by the lid.

Since H6XDI is already impregnated into the low dielectric constant film20, when the water vapor permeates into the low dielectric constant film20, hydrolysis occurs as described above. Thus, a polymerizationreaction occurs immediately to produce polyurea. Therefore, the pores 21in the low dielectric constant film 20 are filled with the polyurea. InFIGS. 1A to 1D, for the sake of convenience in illustration, the statein which the pores 21 are filled with a raw material monomer (liquid ofH6XDI in this example) is indicated by “dots” and the state in which thepores 21 are filled with polyurea is indicated by “oblique lines.”

Subsequently, the wafer W is heated to remove residue existing in thelow dielectric constant film 20 (FIG. 7C). The heating temperature isset to 200 degrees C. or higher, for example, 250 degrees C. The waferis heated in an inert gas atmosphere, for example, a nitrogen gasatmosphere. For example, as shown in FIG. 11, this process may becarried out by mounting the wafer W on the mounting table 52 inside theprocessing container 51 and heating the wafer W with an infrared lamp 54provided inside a lamp house 53. In FIG. 11, reference numeral 55denotes a transmission window, reference numeral 56 denotes a supplypipe for supplying a nitrogen gas, and reference numeral 57 denotes anexhaust pipe. A processing atmosphere at that time is, for example, anatmospheric pressure atmosphere, but may be a vacuum atmosphere.

After the pores 21 of the low dielectric constant film 20 are filledwith the polyurea, a step of forming a via-hole and a trench (groove forburying a wiring) is performed on the low dielectric constant film 20.Prior to this step, a sealing film 60 is formed on the low dielectricconstant film 20 (FIG. 1D). The sealing film 60 is formed to enhance theheat resistance of the polyurea (hatched portion) inside the pores 21which is a protective layer. Accordingly, the sealing film 60 is formedat a temperature lower than a temperature at which the polyurea(polymer) is depolymerized, for example, at 250 degrees C. or lower.

In this example, the sealing film 60 is a polyimide film. For example,the sealing film 60 is formed at a temperature of 150 to 200 degrees C.in a vacuum atmosphere by vapor deposition using a mixed gas ofpyromellitic anhydride (PMDA) and 4,4′-oxydianiline (ODA). A filmthickness of the sealing film 60 is, for example, 100 nm. The polyimidefilm may be formed by coating a chemical solution, instead of the vapordeposition method. Since the polyurea in the pores 21 is exposed on thesurface of the low dielectric constant film 20, it can be said that thesealing film 60 is formed so as to cover a portion where the protectivelayer (polyurea) is exposed.

After forming the sealing film 60, as shown in FIG. 2E, a silicon oxidefilm 65 is formed on the surface of the sealing film 60 by CVD (ChemicalVapor Deposition), for example, in a vacuum atmosphere and at a processtemperature of 300 degrees C. The silicon oxide film 65 is formed, forexample, by allowing vapor of an organic silicon raw material to reactwith an oxidizing gas such as oxygen or ozone. The silicon oxide film 65plays a role of a pattern mask (hard mask) during the etching to bedescribed later. The film formation process of the silicon oxide film 65corresponds to a process performed on the wafer W at a temperaturehigher than the temperature at which the protective layer isdepolymerized.

Subsequently, a hard mask 61, which is a pattern mask for etching madeof, for example, a TiN (titanium nitride) film which has an openedportion corresponding to the trench, is formed by a well-known method(FIG. 2F).

Subsequently, a masking film 62 serving as a mask when etching thevia-hole is formed on the hard mask 61 (FIG. 2G). Further, anantireflection film 63 and a resist film 64 are laminated on the maskingfilm 62 in the named order (FIGS. 2H and 3I). For example, an organicfilm containing carbon as a main component is used as the masking film62. This organic film is obtained by spin-coating a chemical solution onthe wafer W inside an apparatus for forming the antireflection film 63and the resist film 64 to form a resist pattern.

Thereafter, a resist pattern is formed by exposing and developing theresist film 64 so as to form an opening 641 in a portion correspondingto the via-hole (FIG. 3J). Using this resist pattern, the antireflectionfilm 63 is etched by, for example, a CF-based gas (FIG. 3K).Subsequently, using the antireflection film 63 as a mask, the maskingfilm 62 is etched by, for example, the plasma obtained by converting anoxygen gas into plasma. At this time, the resist film 64 is also etchedand removed (FIG. 3L). In this manner, an opening 621 is formed at aposition corresponding to the via-hole in the masking film 62.

Subsequently, using the masking film 62 as an etching mask, the lowdielectric constant film 20 is etched to form a via-hole 201 (FIG. 4M).As a technique of etching the low dielectric constant film 20, namelythe SiOC film in this example, the etching may be performed by plasmaobtained by converting a C₆F₆ gas into plasma. In this case, a smallamount of oxygen gas may be added.

Thereafter, the etching stopper film 13 at the bottom of the via-hole201 is removed by etching. In the case where the etching stopper film 13is, for example, an SiC film, this etching may be performed by, forexample, plasma obtained by converting a CF₄ gas into plasma.Subsequently, the masking film 62 is removed by ashing with plasmaobtained by converting an oxygen gas into plasma (FIG. 4N).

Subsequently, similar to the process of forming the via-hole 201, thelow dielectric constant film 20 is etched using the hard mask 61 to forma trench 202 in a region surrounding the via-hole 201 (FIG. 4O).Thereafter, a barrier layer, for example, a barrier layer 70 a composedof a laminated film of Ti and TiON and configured to prevent copper as aconductive path described below from diffusing into the low dielectricconstant film 20 as an interlayer insulating film, is formed on innersurfaces of the via-hole 201 and the trench 202 (FIG. 4P). Thereafter,the via-hole 201 and the trench 202 are filled with copper (FIG. 5Q).The excess copper, the barrier layer 70 a, the sealing film 60, thesilicon oxide film 65 and the hard mask 61 are removed by CMP (ChemicalMechanical Polishing) to form a copper wiring 70, whereby theupper-layer-side circuit portion is formed (FIG. 5R).

In the above, it is necessary that each process performed thus far iscarried out at a temperature lower than the temperature at which thepolyurea is depolymerized. Then, the polyurea which is a fillingmaterial filling the pores 21 of the low dielectric constant film 20 isremoved (FIG. 5S). When heated at 300 degrees C. or higher, for example,350 degrees C., the polyurea is depolymerized to amine and is evaporated(FIG. 7D). In order not to adversely affect an element portion alreadyformed on the wafer W, particularly a copper wiring, the polyurea may beheated at a temperature of less than 400 degrees C., for example 390degrees C. or lower, for example 300 to 350 degrees C. A period of timeduring which the polyurea is depolymerized, for example, a period oftime during which the polyurea is heated at a temperature of 300 to 400degrees C., may be, for example, 5 minutes or less from the viewpoint ofsuppressing thermal damage to an element. As a heating method, aninfrared lamp may be used as described above, or the wafer W may beheated by mounting the wafer W on the mounting table having a built-inheater. The heating atmosphere is, for example, an inert gas atmospheresuch as a nitrogen gas atmosphere or the like.

In the above-described embodiment, isocyanate and moisture aresequentially supplied to the low dielectric constant film 20 to fill thepores 21 of the low dielectric constant film 20 with the polyurea whichis a polymer having urea bonds, thereby forming a protective layer forprotecting the low dielectric constant film 20. In this state, the lowdielectric constant film 20 is etched to form the via-hole 201 and thetrench 202, and the ashing of the etching mask is performed.Accordingly, in this example, the low dielectric constant film 20 isprotected by the polyurea at the time of etching and ashing performed asplasma treatments. Thus, the occurrence of damage to the low dielectricconstant film 20 is suppressed.

Furthermore, the film-forming temperature of the silicon oxide film 65is, for example, 300 degrees C. which is higher than thedepolymerization temperature of the polyurea. However, the sealing film60 is formed on the low dielectric constant film 20 (the protectivelayer) filled with the polyurea. Therefore, the depolymerization of thepolyurea is suppressed, and the function of the protective layer is notimpaired. Since the polyurea is depolymerized at a temperature of about300 degrees C., when the polyurea is removed from the low dielectricconstant film 20, there is a risk of adversely affecting the elementportion, particularly the copper wiring, already formed on the wafer W.In addition, since the removal of the polyurea can be performed only bythe heat treatment, the method is simple.

The sealing film 60 is not limited to the polyimide film but may be ametal film or an insulating film as long as it can be formed at atemperature lower than the temperature at which the polyurea isgenerated. Examples of the metal film may include a TiN film, a TaN filmand the like. The metal film may be formed by an electroless platingmethod or the like. Furthermore, examples of the insulating film mayinclude a silicon oxide film formed by reacting an aminosilane-based gasand an oxidizing gas such as ozone or the like with each other in avacuum atmosphere, and the like. In this case, the silicon oxide filmmay be formed at a low temperature of, for example, 250 degrees C. Whenthe insulating film is used as the sealing film 60, for example, amethod of coating a coating liquid containing a precursor of theinsulating film on the wafer W may be adopted.

In the above-described embodiment, isocyanate is spin-coated on thewafer W. Alternatively, isocyanate mist may be supplied in a state inwhich the wafer W is stopped.

In the above-described embodiment, the polyurea film is produced by theself-polymerization of isocyanate. Alternatively, as shown in an examplein FIG. 12, the polyurea film may be produced by copolymerization usingisocyanate and amine. R is, for example, an alkyl group (linear alkylgroup or cyclic alkyl group) or an aryl group, and n is an integer oftwo or more.

In this case, it may be possible to adopt, for example, a method inwhich the liquid of one of isocyanate and amine is supplied to the waferby a spin coating method as described above to allow the liquid topermeate into the low dielectric constant film, and then the liquid ofthe other of isocyanate and amine is similarly supplied to the wafer bya spin coating method to allow the liquid to penetrate into the lowdielectric constant film. Alternatively, the isocyanate and the aminemay be, for example, alternately supplied multiple times so that theyare sequentially supplied to the wafer in the form of a gas (vapor). Inthis case, for example, the vapor of isocyanate diffuses into andadsorbs to the pores of the low dielectric constant film, and then thevapor of the amine diffuses into the pores to generate a polymerizationreaction. Such an action is repeated so that the pores are filled with apolyurea film.

Since the polyurea itself is a solid and cannot be converted into aliquid, the method is adopted in which raw materials to become polyureaare separately supplied to the film as described above to producepolyurea in the film.

In the method using the vapors of raw material monomers, the vaporpressures of the raw material monomers may be far apart from each other,for example, different from each other by one digit or more. The reasonfor this is that in a combination of vapor pressures close to eachother, for example, when diffusing amine into the pores of the lowdielectric constant film, the amine is adsorbed onto surfaces of thepores, as a result of which the reaction efficiency of the amine withthe isocyanate deteriorates.

Examples of combinations in which the difference in vapor pressurebetween isocyanate and amine is one digit or more may include an examplein which a skeleton molecule obtained by removing an isocyanatefunctional group from isocyanate and a skeleton molecule obtained byremoving an amine functional group from amine are the same, namely anexample in which isocyanate and amine are provided with the sameskeleton molecule. For example, the vapor pressure of H6XDA to which anamine functional group is bonded is higher by one digit or more than thevapor pressure of H6XDI which is the same skeleton molecule as theskeleton molecule of H6XDA and to which an isocyanate functional groupis bonded.

As shown in FIGS. 13A to 13D, mono-functional molecules may be used asthe raw material monomers. Furthermore, as shown in FIGS. 14A and 14B,isocyanate and secondary amine may be used. The bond contained in apolymer produced in this case is a urea bond.

A raw material monomer having a urea bond may be polymerized to obtain apolyurea film. In this case, the raw material monomer may be supplied tothe low dielectric constant film in the state of liquid, mist or vapor.FIG. 15 shows such an example, in which polymerization is generated toform a polyurea film by irradiating a raw material monomer with light,for example, ultraviolet rays, and giving light energy to the rawmaterial monomer. If the polyurea film is heated at, for example, 350degrees C., the polyurea film is depolymerized into isocyanate andamine.

FIG. 16 shows a CVD apparatus for reacting a raw material monomer with agas to produce (vapor-deposition polymerize) polyurea inside the lowdielectric constant film 20. Reference numeral 70 denotes a vacuumcontainer which defines a vacuum atmosphere. Reference numerals 71 a and72 a denotes raw material supply sources for accommodating isocyanateand amine as raw material monomers in a liquid state, respectively. Theisocyanate liquid and the amine liquid are vaporized by vaporizers 71 cand 72 c installed in supply pipes 71 b and 72 b, respectively. Therespective vapors are introduced into a shower head 73 which is a gasdischarge part. The shower head 73 has a number of discharge holesformed on the lower surface thereof and is configured to dischargeisocyanate vapor and amine vapor from the separate discharge holes tothe processing atmosphere. A wafer W is mounted on a mounting table 74equipped with a temperature adjustment mechanism. First, the isocyanatevapor is supplied to the wafer W, whereby the isocyanate vapor enters alow dielectric constant film formed on the wafer W. Subsequently, thesupply of isocyanate vapor is stopped, and the interior of the vacuumcontainer 70 is evacuated. Thereafter, the amine vapor is supplied tothe wafer W. The isocyanate remaining in the low dielectric constantfilm reacts with the amine to produce polyurea.

Second Embodiment

A second embodiment of the present disclosure will be described. Thisembodiment is an embodiment in which the present disclosure is appliedto a process of forming a RAM, and is an example in which damage causedby over-etching of electrodes is prevented by a protective layer made ofpolyurea.

FIGS. 17A to 17D shows a state in which a memory element film 83 forforming a memory element is formed on an electrode 82 of alower-layer-side circuit surrounded by an insulating film 81, anelectrode film 84 is formed on the memory element film 83, and aprotective layer (polyurea film) 85 made of polyurea is formed on theelectrode film 84. Examples of the memory element may include a ReRAM, aPcRAM, an MRAM and the like. Examples of the memory element film 83 mayinclude a metal oxide film used for a ReRAM (resistance change typememory).

The electrode film 84 is formed of, for example, a laminated film inwhich a titanium nitride (TiN) film and a tungsten (W) film arelaminated in the named order from below.

The protective layer (polyurea film) 85 made of polyurea is produced by,for example, copolymerization using isocyanate and amine as shown inFIG. 12 described above. A thickness of the protective layer 85 is setto, for example, 20 nm to 50 nm. In this case, as an apparatus forproducing the protective layer, the above-mentioned CVD apparatus shownin FIG. 16 may be used.

Subsequently, a mask film (hard mask) 86 is formed on the protectivelayer 85 (FIG. 18E). Examples of the mask film 86 may include a boron(B)-containing silicon film. The boron (B)-containing silicon film isformed using, for example, a silane-based gas and a B₂H₆ gas which is adoping gas. Thereafter, a resist pattern is formed on the mask film 86to form a pattern on the mask film 86. Using the mask film 86 as a hardmask, the protective layer 85, the electrode film 84 and the memoryelement film 83 are etched to transfer the pattern thereto (FIG. 18F).

Subsequently, a sealing film 87 made of, for example, a polyimide film,is formed so as to cover an upper surface and a side surface of alaminate including the mask film 86, the memory element film 83, theelectrode film 84 and the protective layer 85 (FIG. 18G). As describedin the first embodiment, the sealing film 87 is used for suppressingdepolymerization when heated at a temperature higher than thetemperature at which the protective layer 85 is depolymerized.

Furthermore, an insulating film, for example, a silicon oxide film 88 isformed as an element separation film for electrically separatingelements from each other, around the laminate including the memoryelement film 83, the electrode film 84 and the protective layer 85,thereby creating a state in which the laminate is buried in the siliconoxide film 88 (FIG. 18H). The silicon oxide film 88 is formed, forexample, by CVD at a process temperature of 300 degrees C. in a vacuumatmosphere. The process of forming the silicon oxide film 88 correspondsto a process performed on the wafer W at a temperature higher than thetemperature at which the protective layer is depolymerized.

Subsequently, a portion corresponding to the laminate in the siliconoxide film 88 is etched with an etching gas to reach the protectivelayer 85, thereby forming a contact hole 89 (FIG. 19I). Thereafter, theprotective layer 85 is heated to depolymerize polyurea, thereby removingthe protective layer 85 (FIG. 19J). As the step of depolymerizingpolyurea, the same method as described in the first embodiment may beadopted. Then, a metal serving as a conductive path, for example,copper, is embedded in the contact hole 89. Excess metal is removed byCMP to form a conductive path 91, thereby manufacturing a memory element(FIG. 19K).

According to the above-described embodiment, the following effects maybe obtained. In the absence of the protective layer 85, when the contacthole 89 is opened by dry etching, the surface of the electrode film 84is oxidized by the over-etching of the mask film 86, whereby a damagedlayer is formed. Therefore, the damaged layer is interposed at aninterface between the electrode film 84 and the conductive path 91,which may adversely affect the electric characteristics. In contrast, inthe above-described embodiment, the protective layer 85 is formed on thesurface of the electrode film 84 and may be removed by heat. It istherefore possible to prevent a damaged layer from being formed on thesurface of the electrode film 84.

After the protective layer 85 is formed, the insulating film 88 isformed at a temperature equal to or higher than the depolymerizationtemperature of the polyurea. Since the protective layer 85 is coveredwith the sealing film 87, the depolymerization of polyurea is suppressedso that the function of the protective layer 85 is not impaired.

The method of producing the protective layer 85 is not limited to CVD,but may be the liquid processing described with reference to FIG. 9 inthe first embodiment. Alternatively, the method of producing theprotective layer 85 may be a method performed using a coating apparatusshown in FIG. 20. In FIG. 20, portions corresponding to the referencenumerals shown in FIG. 9 are denoted by the same reference numerals.Reference numeral 38 a denotes a supply source of a chemical solution,for example, H6XDI, and reference numeral 38 b is a supply source of achemical solution, for example, 1,3-bis (aminomethyl) cyclohexane(H6XDA). The coating apparatus is configured so that these chemicalsolutions are joined immediately before the nozzle 38 and a mixed liquidthereof is supplied to the central portion of the wafer W. As the waferW rotates, the mixed liquid spreads on the wafer W, whereby theprotective layer 85 which is a polyurea film is formed. In addition, asshown in FIG. 20, a heating part 39 composed of, for example, a lightemitting diode, is disposed below the wafer W. The wafer W is heated bythe heating part 39 to promote polymerization.

The raw material used for forming the protective layer 85 is not limitedto the above-mentioned example, but may be, for example, theabove-mentioned raw materials shown in FIGS. 13A to 15.

EXAMPLE Evaluation Test 1

A low dielectric constant film made of a SiOC film was formed on a barewafer. Absorption spectra were measured for each of a low dielectricconstant film before filling of polyurea, a low dielectric constant filmafter filling of polyurea and a low dielectric constant film afterremoving of polyurea. The measurement results are as shown in FIG. 21.In FIG. 21, curves (1) to (3) correspond to before filling of polyurea,after filling of polyurea, and after removing of polyurea, respectively.In curve (2) obtained after filling of polyurea, peaks corresponding toan NH bond (indicated by arrow a), a CH bond (indicated by arrow b), aCO bond (indicated by arrow c) and a CN bond (indicated by arrow d) areillustrated. However, in curve (1) obtained before filling of polyureaand curve (3) obtained after removing of polyurea, these peaks are notseen.

From these results, it was confirmed that polyurea is filled into thepores of the low dielectric constant film by the method described in thefirst embodiment, and further that polyurea is not left in the lowdielectric constant film by performing the polyurea removal process.

Evaluation Test 2

Polyurea films were formed on surfaces of two substrates each having asquare shape with a side length of 5 cm by the vacuum depositiondescribed above. These substrates were stacked and heated in a nitrogengas atmosphere at 350 degrees C. for 5 minutes. During this heattreatment, the absorption spectrum was measured by infrared absorptionspectroscopy (IR) on a rear surface (lower surface) of the uppersubstrate and a front surface (upper surface) of the lower substrate,respectively. The measurement results are shown in FIG. 22. The spectrumof the rear surface of the upper substrate is indicated by a solid linewaveform, and the spectrum of the front surface of the lower substrateis indicated by a dotted line waveform. Each of these spectra shows thata polyurea film is present at the measured location. In addition, whenviewed visually, a polyurea film seems to be present on the rear surfaceof the upper substrate and on the front surface of the lower substrate.No polyurea film is seen on the front surface of the upper substrate andon the rear surface of the lower substrate.

From the state of the front surface of the upper substrate, it wasconfirmed that the polyurea film can be removed by heating therespective substrate. Since the polyurea film disappears on the frontsurface of the upper substrate in this manner, it is considered that thepolyurea film formed between the upper substrate and the lower substrateis prevented from disappearing during the hearing because the polyureafilm is sandwiched between the two substrates. The reason for this isthat there is a presumption that depolymerization is suppressed becausethere is no escape place of a monomer produced by depolymerization.Accordingly, it was confirmed that, by forming the sealing film on thepolyurea film (protective layer) as described above, the protectivelayer does not disappear even if the heating temperature is higher thanthe temperature at which depolymerization should occur.

Evaluation Test 3

A polyurea film having a film thickness of 400 nm was formed on a squaresilicon substrate having a side length of 6 cm, and then the polyureafilm was heated in a nitrogen gas atmosphere for 5 minutes. The heatingtemperature was set in increments of 50 degrees C. in a range from 150degrees C. to 450 degrees C. The film thickness of the polyurea filmafter the heat treatment (annealing) was measured. The result shown inFIG. 23 was obtained. From this result, it can be seen that the polyureafilm is not depolymerized at 250 degrees C., but depolymerizationgreatly proceeds at 300 degrees C. so that the polyurea film completelydisappears at 350 degrees C.

Evaluation Test 4

Four square silicon substrates having a side length of 6 cm wereprepared, and a polyurea film having a film thickness of 400 nm wasformed on each of the silicon substrates. Polyimide films having filmthicknesses of 10 nm, 30 nm and 70 nm, respectively, were formed on thepolyurea films of the three substrates. A polyimide film was not formedon the remaining one substrate. These four samples were thermallytreated at 300 degrees C. for 5 minutes in a nitrogen gas atmosphere,and then absorption spectra were measured by infrared absorptionspectroscopy (IR). The measurement results are shown in FIG. 24. In FIG.24, curve (1) corresponds to a substrate on which no polyimide film isformed, curve (2) corresponds to a substrate on which a polyimide filmis formed with a film thickness of 10 nm, curve (3) corresponds to asubstrate on which a polyimide film is formed with a film thickness of30 nm, and curve (4) corresponds to a substrate on which a polyimidefilm is formed with a film thickness of 70 nm. Since the position of thewave number of a CH bond or the like in the absorption spectra hasalready been explained in the section of evaluation test 1, the sameexplanation for FIG. 24 is omitted.

From these results, it can be seen that when the thickness of thepolyimide film as a sealing film is 10 nm or 30 nm, the degree ofdepolymerization of the polyurea film is somewhat smaller than when thepolyimide film is not formed, but depolymerization proceedsconsiderably. In contrast, it can be noted that when the thickness ofthe polyimide film is 70 nm, the depolymerization of the polyurea filmdoes not occur.

Evaluation Test 5

Four kinds of samples similar to the samples used in evaluation test 4were prepared. That is to say, a sample in which a sealing film is notformed on a polyurea film and three kinds of samples in which polyimidefilms having film thicknesses of 10 nm, 30 nm and 70 nm are formed onrespective polyurea films were prepared. With respect to the respectivesamples, the heating temperatures were set at four levels of 250 degreesC., 275 degrees C., 300 degrees C. and 325 degrees C., and heattreatments were performed at the respective heating temperatures for 5minutes.

For these samples, absorption spectra were measured by infraredabsorption spectroscopy, and the peak value of a CH bond correspondingto the skeleton of the polyurea film was obtained. Then, a ratio of thepeak value after the heat treatment to the peak value before the heattreatment was obtained. The ratio of the peak value was plotted for eachheat treatment temperature to obtain a graph of FIG. 25. In FIG. 25, PIis an abbreviation for the polyimide film. For the sake of convenience,the ratio of the peak value will be referred to as bond remaining rate.

For the sample having a heating temperature of 300 degrees C., the peakvalue of a C═O bond corresponding to a urea bond was also obtained.Then, for each of the CH bond peak value and the C═O bond peak value, aratio of the peak value after the heat treatment to the peak valuebefore the heat treatment was obtained. A relationship between thethickness of the polyimide film and the ratio of the peak values wasobtained. The results are as shown in FIG. 26.

From these results, it is understood that when the polyimide film isformed on the polyurea film, if the polyimide film is 70 nm in the aboveexample, depolymerization does not occur even when heated to 300 degreesC. Therefore, it is understood that the polyimide film is effective as asealing film capable of suppressing depolymerization with respect to thepolyurea film.

Evaluation Test 6

A relationship between the film thickness and the heat resistance wasinvestigated for the polyurea film on which the polyimide film is notlaminated. Polyurea films were formed on silicon substrates with filmthicknesses of 280 nm, 360 nm and 3,000 nm, respectively. For therespective samples, heat treatments were performed for 5 minutes whilechanging the heating temperature. With respect to the films formed onthe respective substrates before and after the heat treatments,absorption spectra were measured by infrared absorption spectroscopy.

For the CH bond, a ratio of the peak value after the heat treatment tothe peak value before the heat treatment (CH bond remaining rate) ineach sample was obtained. A relationship between a CH bond remainingrate and the heating temperature was obtained for each thickness ofpolyurea. The results are shown in FIG. 27. In addition, when theheating temperature is 300 degrees C., the film thickness of thepolyurea film and the respective remaining rates of the CH bond and theC═O bond were obtained. The results are shown in FIG. 28.

From these results, it was found that even if the film thickness of thepolyurea film is increased, the improvement of heat resistance cannot beexpected.

According to the present disclosure, a protective layer composed of apolymer having a urea bond is formed on a surface of a substrate onwhich a protected film to be protected is formed. The protective layeris sealed with a sealing film, thereby improving the heat resistance ofthe protective layer. Thereafter, a process of applying damage to theprotected film is performed (in the absence of a protective layer).Then, the substrate is heated to depolymerize the polymer. Thus, even ifa process that may apply damage to the protected film is performed, itis possible to suppress damage to the protected film, because theprotective layer is present.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosures. Indeed, the embodiments described herein maybe embodied in a variety of other forms. Furthermore, various omissions,substitutions and changes in the form of the embodiments describedherein may be made without departing from the spirit of the disclosures.The accompanying claims and their equivalents are intended to cover suchforms or modifications as would fall within the scope and spirit of thedisclosures.

What is claimed is:
 1. A method of manufacturing a semiconductor deviceby performing a process on a substrate, comprising: forming a protectivelayer made of a polymer having a urea bond by supplying a raw materialfor polymerization to a surface of a substrate on which a protected filmto be protected is formed; forming a sealing film at a first temperaturelower than a second temperature at which the polymer is depolymerized,so as to cover a portion where the protective layer is exposed; afterthe forming a sealing film, subjecting the substrate to a treatment at athird temperature equal to or higher than the second temperature atwhich the polymer as the protective layer is depolymerized; after thesubjecting the substrate to a treatment at a third temperature,performing a treatment which causes damage to the protected film whenthe protective layer is not present; and after the performing atreatment which causes damage to the protected film, depolymerizing thepolymer by heating the substrate, wherein the protected film is a porouslow dielectric constant film and the protective layer includes a polymerembedded in pores of the low dielectric constant film, and wherein theforming the protective layer includes impregnating the low dielectricconstant film with a liquid or a mist of isocyanate and supplyingmoisture to the low dielectric constant film to hydrolyze the isocyanateto produce an amine, and heating the substrate to polymerize theisocyanate and the amine.
 2. The method of claim 1, wherein thesubjecting the substrate to a treatment at a third temperature equal toor higher than the second temperature at which the polymer isdepolymerized includes forming a thin film on the sealing film, and theperforming a treatment which causes damage to the protected film is aplasma process for forming a recess in the low dielectric constant film.3. The method of claim 1, wherein the forming the protective layerincludes impregnating the low dielectric constant film with the liquidor mist of the isocyanate and then bringing an atmosphere in which thesubstrate is placed into a water vapor atmosphere.
 4. The method ofclaim 1, wherein the forming the protective layer includes sequentiallydiffusing one and the other of a vapor of isocyanate and a vapor ofamine into the low dielectric constant film and heating the substrate topolymerize the isocyanate and the amine.
 5. A method of manufacturing asemiconductor device by performing a process on a substrate, comprisingthe steps of: forming a protective layer made of a polymer having a ureabond by supplying a raw material for polymerization to a surface of asubstrate on which a protected film to be protected is formed, whereinthe protected film is an electrode film made of a metal or a metalcompound; etching the protective layer and the electrode film by forminga pattern mask film on the protective layer formed on the electrodefilm; forming a sealing film at a first temperature lower than a secondtemperature at which the polymer is depolymerized, so as to cover aportion where the protective layer is exposed; after the forming asealing film, subjecting the substrate to a treatment at a thirdtemperature equal to or higher than the second temperature at which thepolymer as the protective layer is depolymerized; after the subjectingthe substrate to a treatment at a third temperature, performing atreatment which causes damage to the protected film when the protectivelayer is not present; and after the performing a treatment which causesdamage to the protected film, depolymerizing the polymer by heating thesubstrate wherein the forming a sealing film includes, after theetching, covering the entirety of a laminate composed of the patternmask film, the protective layer and the electrode film with the sealingfilm which is a first insulating film, wherein the subjecting thesubstrate to a treatment at a third temperature equal to or higher thanthe second temperature at which the polymer is depolymerized includesforming a second insulating film from above the sealing film, andwherein the performing a treatment which causes damage to the protectedfilm includes forming a contact hole reaching the protective layer byetching the second insulating film formed on the sealing film, and thesealing film.
 6. The method of claim 5, wherein a memory element film isformed below the electrode film, and the memory element film is etchedin the etching the electrode film.
 7. The method of claim 5, wherein theforming the protective layer includes supplying a vapor of isocyanateand a vapor of amine to the substrate, and heating the substrate topolymerize the isocyanate and the amine.
 8. The method of claim 5,wherein the forming the protective layer includes supplying a liquid ofisocyanate and a liquid of amine to the substrate, and heating thesubstrate to polymerize the isocyanate and the amine on the surface ofthe substrate.